1. Field of the Invention
The present invention relates to an operating circuit for an X-ray tube for use with a high-voltage generator and a switch mechanism for connecting and disconnecting the X-ray tube to the high-voltage generator.
2. Description of the Prior Art
In X-ray diagnostics systems, a low power X-ray tube is used in certain operating modes, for example, in the transillumination mode and in a fluoroscopic pulsed mode. In these low power modes, X-ray tube currents or only a few milliamperes are used dependent on the X-ray tube voltage. As a consequence of the capacitances in the high-voltage circuit (high-voltage cable and smoothing capacitors in the high-voltage transformer), the X-ray tube voltage decays based on a small function of e, where e is the natural logarithm base, after the high-voltage is disconnected. The time constant of the decay depends on the size of the capacitance and on the internal resistance of the X-ray tube, i.e., on the adjusted X-ray tube current. The unavoidable presence or X-ray tube current, therefore, causes an additional radiation load on the patient in the form of a relatively large dose of low-energy radiation during the decay time of the X-ray tube voltage.